From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Clutch destruction tests, wear rates, and performance issues for 20/25 and Bentley models.
Identifier | ExFiles\Box 85\2\ scan0078 | |
Date | 23th May 1934 | |
CLUTCHES - 20/25 & BENTLEY. In the attached report on Clutch destruction tests carried out on the test bed the rate of wear of various types of linings fitted to the standard clutch is compared with the behaviour of the new 20/25 clutch. These tests were originated when we were trying to find a lining that would have a longer life in the Bentley. Apart from that it seems possible that we have discovered a cause of the complaints of clutch slip on the 20/25; namely, that a new lining when first heated to about 400°F.{Mr Friese} drops in coefficient of friction to under .15 until reheated to a higher temperature. The heat and chemical treatments were tried to overcome this fault. We can say however from these tests that the life of a bonded lining is inversely proportional to its freedom from slipping. On the new clutch the rate of wear of a bonded lining is negligible and we do not think that the standard lining RAD.11 will ever reach a temperature on the road to cause slipping. We wish to use this lining and not the chemically treated one as the latter has on 3 cars given a less smooth take up. The first of the new type clutches fitted to 21-G-IV suffered from two troubles, (1) a flywheel vibration at 3000 r.p.m. and (2) violent jagger when starting from rest, particularly on a gradient. The first was overcome by thinning the back plate to the attached EX.14076. For the jaggers we tried varying spring loads and movement of the inner pressure plate without affecting the trouble. Next we tried a staggered driven member, to which was rivetted the Ferodo in sections with .025 set, in conjunction with .012 movement of the inner plate. This provided a perfect get-away. As .037 of the separation was wasted the clutch did not stop too readily. The .012 movement of the inner plate was removed, the take up of the clutch remaining fair but not as good as previously. | ||